Last weekend, I made a little zip-line for the kids. 40' long, very shallow angle—maybe -4 degrees. They could get a running start and go about half way. It was not zippy. But, they were having fun. After about an hour, I noticed that the pulley was not turning. I grabbed another. It was seized, too. Both were seized. Solid. Couldn't budge them.

They were both Mad Rock 3" Rescue Pulleys. Both had bushings and were cheap, $20 each. I never expected much from them, but didn't expect them to seize the first time they were used.

Of course, bushing pulleys are not good for zip-lines, but like I said, no zipping was happening.

Anyone ever seen two pulleys seize on at the same time? Sounds like a bad batch to me. Mad Rock has discontinued them, but offered a refund if I send them back. Awesome!

Rather annoying to have those pulleys seize solid for no apparent reason. I've occasionally seen similar problems with nylon sheave pulleys, and I'm led to believe one Camp model (the "small mobile") is known for this too. But not a 3 inch metal sheave so-called "rescue pulley."

I've had to fix slightly stiff rescue pulleys before, although admittedly mine are bearing ones. Spraying liberally with contact cleaner or a similar solvent and then applying a little lubricant seemed to do the trick. My most abused one (left outside on a zip line for extended periods) has and bolt-and-nut axle and is easily disassembled.

A better suggestion for a zip line pulley is something designed for the job - a tandem carriage like this.